Methods and machines for sorting articles have been known in the art for many years and are useful for separating desirable and undesirable articles from a product stream using a variety of methods. The machines found in the art include types that utilize reflecting electromagnetic radiation in the form of light to determine the optical reflective characteristics of the articles in the product stream using color as a determinant. A notable example of such a sorter is the High Speed Mass Flow Sorting Apparatus for Optically Inspection and Sorting Bulk Food Products as shown in U.S. Pat. No. 5,887,073 assigned to Key Technology, Inc. Another notable example of an exemplary sorter is shown in copending patent application Ser. No. 11/392,947 filed on Mar. 30, 2006 the disclosures of which are incorporated by reference herein.
Some methods and machines for sorting articles utilize emitted light from articles to be sorted in an effort to make a determination between desirable and undesirable articles. Often, it is desirable for a sorting apparatus to include an ability to distinguish between organic and inorganic articles. It is known in the art that chlorophyll produces a fluorescence emission in response to an excitation wavelength. Chlorophyll is an essential molecule during photosynthesis and is present in varying forms in many plants, including many comestible articles such as green beans and peas.
An example of a machine or method that exploits this property is disclosed in U.S. Pat. No. 6,734,383. Here, light is cast onto articles in a product stream and a passed in front of a fluorescent or backlit background element. In this example, the emission from the background is selected to be within an order of magnitude of the emission of the desirable articles which are presumed to emit light due to their chlorophyll response. This approach provides a clear distinction between desirable articles that emit light and undesirable non-emitting articles, effectively reducing a sorting decision to a basic thresholding operation.
This approach, while simple, suffers from a number of shortcomings. One specific shortcoming that limits the widespread application of this machine or method is the fact that different types of articles, varieties of articles, and even the manner in which the articles are prepared can have a profound impact on the magnitude of the light that is emitted by fluorescence from the articles. This reality requires that the background element be carefully selected or tuned for a specific application. In a typical food processing line, it is common that multiple types of articles, varieties of articles, and methods of treatment of the articles are utilized over the course of operation to satisfy both the supply and market needs. This situation requires that the machine operator have at their disposal an appropriate background element for each situation. In addition, this presents an additional burden on the manufacturer of the machine to design and produce a family of background elements, each tuned to a specific situation.
The present invention overcomes this and other limitations of the prior art, and is equipped with a background element that does not fluoresce or emit light. The invention utilizes an expanded capability of gathering and manipulating light emitted and returned by articles in a product stream, and light returned by a passive background element. This expanded capability is realized by devoting one channel of an optical scanner to measuring light emitted from articles, another channel for measuring reflected light from the articles and background element, and another channel for measuring light that is reflected and scattered to some degree by the articles and the background element. A sorting processor receives the measurements from these channels and logically combines them with previously defined and user identified criteria to make a determination whether or not an article is an acceptable or unacceptable article.